1. Field of the Invention
The present invention relates to an electrostatic recording apparatus of a printer, a copier or the like using an electrophotography system, particularly relates to a developing apparatus using a two components developer and an electrostatic recording apparatus using the same.
2. Description of the Related Art
FIG. 8 is an outline view of an electrostatic recording apparatus of an electrophotography system using a developing apparatus of a background art. A developing apparatus 4 includes two developing rollers 31a, 31b at positions opposed to a photosensitive member 1, a carry roller 35 for carrying a developer which is a mixture of a toner 21 and a carrier to the developing rollers 31b, and a carrying amount restricting member 33 for restricting an amount of carrying the developer to a predetermined amount.
An electrostatic latent image formed on the photosensitive member 1 by charging uniformly using a charging apparatus 2 and thereafter exposed in accordance with image information by an exposing apparatus 3 is devloped by the developer on the developing rollers 31a, 31b at a developing region 40a, 40b to thereby adhere the toner 21 to.
The developing apparatus having a constitution in which the developing rollers 31a, 31b are opposed to each other by interposing the carrying amount restricting member 33 as shown by FIG. 8 is generally referred to as a center feed type developing apparatus and is known as a developing system capable of achieving high print quality by a printing apparatus of an electrostatic recording system having a fast printing speed.
Successively, the toner 21 on the photosensitive member 1 is transferred onto a record medium 8 by forming an electric field in a direction of moving the toner 21 to the record medium 8 by a transferring apparatus 7. The record medium 8 adhered with the toner 21 is applied with heat and pressure in passing a fixing apparatus 9, and the toner 21 is melted to fixedly attach to fix to the record medium 8.
An adhered toner 21 or a paper powder or the like remaining on the photosensitive member 1 after passing the transferring portion is removed from the photosensitive member 1 by a cleaning apparatus 11.
Next, operation of the developing apparatus 4 will be explained. Inside of the developing apparatus 4 is arranged with two pieces of the developing rollers 31a and 31b having rotatable sleeve rollers 32a, 32b at outer peripheries of fixed magnets 30a, 30b to be opposed to each other by interposing the carrying amount restricting member 33.
According to the developing roller 31a, the sleeve roller 32a is rotated in the clockwise direction, that is, such that the developer is rotated in a direction inverse to a direction of rotating the photosensitive member 1 at a developing region 40a (hereinafter, referred to as inverse rotation).
According to the developing roller 31b, the sleeve roller 32b is rotated in the counterclockwise direction, that is, such that the developer is rotated in a direction the same as the direction of rotating the photosensitive member 1 in a developing region 40b (hereinafter, referred to as regular rotation).
A vicinity of the developing roller 31b is provided with the carry roller 35 constituted by a fixed magnet and a sleeve roller arranged rotatably at an outer periphery thereof similar to the developing roller for carrying the developer to the developing roller 31b. 
Further, an agitating mechanism portion 34 surrounded by a broken line is arranged with two augers 36a, 36b by providing intervals between outer peripheries of the augers and a bottom portion and a side portion of the developing apparatus 4, and a toner concentration sensor 45 is arranged such that a detecting face thereof is brought into contact with the developer accumulated at a lower portion of the auger 36b at the bottom portion of the developing apparatus on a lower side of the auger 36b. 
A partition wall 41a is projected from a lower portion of the developing apparatus between the two augers 36a and 36b, and a partition wall 41b is projected also between the auger 36a and the carry roller 35, to form a region of accumulating the developer at lower regions of the respective augers. A partition plate 37 is provided between the two augers 36a, 36b. 
An upper side of the agitating mechanism portion 34 is provided with a toner hopper 39 charged with the toner 21 at inside thereof, and a supply roller 38 for supplying the charged toner 21 into an agitating chamber.
The agitating mechanism portion 34 agitates the developer while moving the developer in a front and rear direction relative to a face of the drawing by rotating the augers 36a, 36b. According to the example, the auger 36a is rotated in the clockwise direction to carry the developer to a depth side of the drawing, the developer is made to flow to a side of the auger 36b at a machine end of the developing apparatus not illustrated, and the auger 36b is rotated in the counter clockwise direction to carry the developer to a front side.
At this occasion, since the partition wall 41a is projected from below to between the augers 36a, 36b, and lower portions of surroundings of the augers 36a, 36b are surrounded by the partition walls 41 and the bottom portion of the developing apparatus, the developer accumulated at the region is pressed in an axial direction and a rotational direction by feeding blades of the augers 36a, 36b, the auger 36a carries the accumulated developer to the depth side of drawing while moving the developer in a direction of the carry roller 35, and the auger 36b carries the developer to the front side while moving the developer to a left side of drawing.
Therefore, the auger 36a carries the developer to the depth side of drawing while moving the developer in the direction of the partition wall 41b and in the carrying procedure, the developer moved in the direction of the carry roller 35 by a magnetic force of the carry roller 35 is adsorbed to the carry roller 35.
The developer adsorbed by the carry roller 35 is carried to a vicinity of the developing roller 31b by rotating the sleeve roller, magnetically adsorbed to a surface of the sleeve roller 32b by a magnetic force of N1 pole of the magnet 30b at inside of the developing roller 31b, and is carried to S1 pole by rotating the sleeve roller 32b. The carrying amount restricting member 33 is arranged by adjusting an interval from the sleeve roller 32b, an amount of carrying the carried developer is restricted by the interval between the carrying amount restricting member 33 and the sleeve roller 32b (hereinafter, referred to as doctor gap) by rotating the sleeve roller 32b, and a constant amount of the developer passing the carrying amount restricting member 33 reaches the developing region 40b. 
Here, the developer is erected by a magnetic field formed by N2 pole and a magnetic pole at a surrounding thereof to slide to abrade the photosensitive member 1. The doctor gap is set to constitute a proper value of a carrying amount relative to a developing gap so as not to disturb a developed image by excessively abrading the photosensitive member 1 by the developer, or to achieve a sufficient printing concentration because the carrying amount is small relative to the interval between the photosensitive member 1 and the sleeve roller 32 (hereinafter, referred to as developing gap).
The developer which cannot pass the doctor gap at the carrying amount restricting member 33 rides over the carrying amount restricting member 33 to be carried to the developing roller 31a and is carried to the developing region 40a by restricting the carrying amount to be constant by the interval between the carrying amount restricting member 33 and the sleeve roller 32a. The developer which cannot pass the doctor gap is returned to the agitating mechanism portion 34 by a carrying guide 50.
The developer carried to the developing region 40b by the sleeve roller 32b to finish developing is carried by rotating the sleeve roller 32b to return to the carry roller 35. Further, the developer carried to the developing region 40a by the sleeve roller 32a to finish developing is carried by rotating the sleeve roller 32a to return to the agitating mechanism portion 34 by the carrying guide 50.
In this way, according to the developing apparatus of the center feed system, two developing rollers 31a, 31b interposing the carrying amount restricting member 33 carry the developer in directions inverse to each other and therefore, a flow of the developer is divided in two. That is, there are a flow of returning from the developing roller 31a to the agitating mechanism portion 34 to direct to a side of the carrying amount restricting member 33 by way of the carry roller 35 and a flow directed from the developing roller 31b to a side of the carrying amount restricting member 33 by way of the carry roller 35. The two flows merge at the carry roller 35, and are mixed to carry to feed to the side of the carrying amount restricting member 33.
The toner concentration sensor 45 provided at inside of the agitating mechanism portion 34 always detects a toner concentration value of the developer carried by the auger 36b and compares a detected value thereof with a reference value when the developer having a rectified toner concentration is carried at a toner concentration control circuit, not illustrated. When the toner concentration is detected to be low, the toner 21 is supplied to the agitating mechanism portion 34 from the toner hopper 39 by rotating the supply roller 38 to agitate to mix with the developer by rotating the auger 36b. 
When the detected value of the toner concentration sensor 45 reaches the specified toner concentration by supplying the toner, supply of the toner 21 is stopped. When the toner concentration does not reach the specified value, the toner 21 is further supplied repeatedly until the toner concentration reaches the specified value.
The supplied toner is agitated while being carried to the front side of the drawing by rotating the auger 36b to be conveyed to the auger 36a at an end portion on the front side while being frictionally charged along with a carrier to be conveyed again to the carry roller 35 while being carried to the depth side of the drawing to circulate at inside thereof in the developing operation to thereby relate to development.
This kind of the developing apparatus is described in, for example, JP-A-5-107909, JP-A-6-167876, JP-A-6-019300, JP-A-7-175309 and JP-A-2002-14533.
In the recording apparatus of the electrostatic recording system for carrying out printing by the above-described process, there is needed development of a small-sized low cost developing system capable of carrying out printing having a high resolution without being adhered with the carrier at a high printing density also on a sheet having a wide width at high speed.
In order to meet such a purpose, there are many examples of adopting the developing apparatus of the center feed system since high image quality printing can easily be carried out, however, as described above, according to the developing apparatus of the center feed system, the flow of the developer at inside of the apparatus is divided in two and therefore, an amount of the developer returned to the agitating mechanism portion 34 after development frequently constitutes a portion of a total thereof.
Although the concentration of the developer returned to the agitating mechanism portion 34 is detected by the toner concentration sensor 45 and when the concentration is lower than the reference value, the concentration is returned to the reference value by supplying the toner 21, a flow of the developer merges with the flow which does not detour the agitating mechanism portion 34 at the carry roller 35, that is, the flow of the developer the concentration of which becomes low without supplying the toner 21 after consuming the toner to mix with each other and therefore, in order to make the toner concentration at a time point of reaching the carrying amount restricting member 33 coincide with the reference value, it is necessary to supply the toner amount to the developer including an amount thereof which is consumed by the flow in which the toner 21 is not supplied.
Further, according to the developing apparatus having members of carrying the developer in axial directions of augers 36a, 36b or the like, there is repeated operation of returning the developer consuming the toner 21 by the developing rollers 31a, 31b to the augers 36a, 36b, kneading the developer with the developer carried by the augers 36b and thereafter carrying to the developing rollers 31a, 31b again to consume the toner 21 and therefore, the toner concentration is significantly lowered on the downstream side in the feeding direction and a large amount of the toner 21 is supplied during a time period of passing the toner supply portion in order to recover the toner concentration of the developer having the considerably lowered toner concentration to the reference toner concentration.
The higher the printing density (printing area per unit area), the wider the printing width and the larger the toner amount consumed at the developing region during a time period by which the developer is moved by a unit length in the axial direction by the fast printing speed, the more significant the inclination of the toner concentration in the axial direction appears.
Although in the developing apparatus 4, the toner 21 supplied from the toner hopper 39 is normally diffused to mix with the developer swiftly by rotating the auger 36b. According to an investigation by the inventors, it has been found that there is a limit in the toner concentration capable of diffusing to mix the supplied toner 21 to inside to the developer to charge the carrier and the toner 21, that is, a mixing rate (hereinafter, referred to as mixing limit toner concentration), and even when the toner exceeding the mixing limit toner concentration is supplied, the toner 21 cannot be brought into the developer and the toner 21 is separated to float on a surface of the developer.
When the floating toner 21 reaches the developing portion by riding on the flow of the developer, the toner 21 stains a printed image as fogging to a background portion, or stains inside of the recording apparatus by being scattered from an opening portion of the developing apparatus to outside of the apparatus.
As a method of preventing the phenomenon, there are known various constitutions of adding the partition plate 37 a lower end of which is disposed on a lower side of the surface of the developer on the side of the developing rollers of the augers 36b supplied with the toner (refer to FIG. 8), and rotating the augers 36a, 36b in rotational directions in directions of storing the developer between the two augers in the constitution of using two pieces of the augers 36a, 36b. However, the once floating toner 21 cannot be brought into the developer and therefore, the stored floating toner flows out from the agitating mechanism portion to be blown out to outside of the developing apparatus at a certain time point.
There are JP-A-5-107909, JP-A-6-167876, JP-A-6-019300, JP-A-7-175309, mentioned above, as inventions for promoting an agitating function, when the augers or the like having the high agitating function are used, although the toner 21 can temporarily be mixed into the developer, when the toner concentration of the agitating mechanism portion 34 exceeds the mixing limit toner concentration, there is a case in which even when the mixing is carried out as much as possible, the toner 21 exceeding an amount of capable of being held in the developer is floated in the procedure of carrying the toner 21 and therefore, a drawback of scattering the toner is rather promoted.
As the invention of controlling the developer carried from the agitating mechanism portion 34 not to exceed a reference toner concentration value, JP-A-2002-14533, mentioned above, discloses a method for providing two pieces of toner concentration sensors on an upstream side and a downstream side of an agitating mechanism portion and changing a toner supply amount by detected values of the two sensors.
However, according to the system, the system of the prior art of comparing an output value of a single toner concentration sensor with a reference toner concentration value and changing a toner amount to be supplied by a difference therebetween is added with an effect of correcting a supply amount when the supply amount is varied from an inherent supply amount, and there is not sufficiently resolved the problem that when a large amount of the toner is consumed in the developing apparatus having the flow which does not pass through the agitating mechanism portion in the developing apparatus, in order to recover the toner concentration to the reference value, a large amount of the toner is supplied to the developer passing the agitating mechanism portion to bring about the drawback of scattering the toner or the like.